Several groups of immunogenic proteins have been isolated from Streptococcus pyogenes by preparative flat bed-isoelectric focusing. Purification by affinity column chromatography has resulted in the separation of the antigens responsible for protection against challenge with homologous and heterologous serotypes of Streptococcus pyogenes. Immune electron microscopy has shown that these antigens are associated with the outer surface of the cell. It thus appears that the "ribosomal immunogen" may be a cell surface protein(s) that binds to the ribosome during the isolation of ribosomes after physical or enzymatic degradation of the cell wall. Furter studies on the purification of these antigens and determination of the reactivity of antibodies to these antigens with host tissue will be continued. Outer membrane proteins from Salmonella typhimurium have been isolated by several procedures. Two immunogenic proteins have been identified by transfer of SDS-PAGE electrophoresis onto nitrocellulose strips. Further studies on purification of these two proteins and their relationship to the outer membrane envelope will be initiated.